Method and apparatus for driving an electrochromic element

ABSTRACT

Provided is an apparatus for driving an electrochromic element having an excellent operating performance, which is capable of controlling, during a transitional state in which a light transmittance changes, a speed and period of the transitional state, the apparatus for driving an electrochromic element being configured to perform, when an absorbance of an electrochromic element is to be increased from a current absorbance to a target absorbance, before normal drive of driving the electrochromic element at a duty ratio (D 1 ) for maintaining the target absorbance, accelerated drive of driving the electrochromic element at a duty ratio (D 2 ) larger than the duty ratio (D 1 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for driving anelectrochromic element.

2. Description of the Related Art

An electrochromic (EC) phenomenon is a phenomenon in which a material iscolored or decolored through changes in its light absorption regioninduced by a reversible electrochemical reaction (oxidation reaction orreduction reaction) caused at the time of application of a voltage. Anelectrochemically coloring/decoloring element utilizing the ECphenomenon is referred to as “electrochromic (EC) element,” and isexpected to find applications as a light control element configured tochange a light transmittance. As the EC element, there have been knownan inorganic EC element using a metal oxide such as WO₃, and an organicEC element using an organic low-molecular compound such as a viologenand an electroconductive polymer. Of those elements, it has been knownthat the organic EC element, in which a low-molecular organic materialis colored/decolored in a solution state, has advantages of a sufficientcontrast ratio in a colored state, a high transmittance in a decoloredstate. In addition, it has been known that the organic EC element has anadvantage in that its color state can be arbitrarily controlled bymixing a plurality of materials having different absorption wavelengths.

In order to use such an EC element in an optical filter, there isrequired a drive method for controlling the light transmittancearbitrarily. Further, it is also required to prevent a significantchange in wavelength selectivity (absorption spectrum) of lightabsorption in the element even at the time of a change in lighttransmittance.

As the drive method for controlling the light transmittance, in JapanesePatent Application Laid-Open No. H11-109423, there is disclosed a pulsewidth modulation (PWM) drive method involving applying, to an inorganicEC element, a voltage for causing an electrochemical reaction as a pulseand controlling a ratio of a duration of voltage application to onecycle of the pulse (duty ratio).

Further, in “Solar Energy Materials & Solar Cells” 104, (2012), pp. 140to 145, there is such a disclosure that an organic EC element formed ofa single type of material is operated through PWM drive. The ratio ofthe duration of voltage application for causing the electrochemicalreaction to one cycle of the pulse (duty ratio) is controlled in thesame manner as in Japanese Patent Application Laid-Open No. H11-109423.Further, there is also such a disclosure that during a remainingduration of the one cycle of the pulse, the voltage application ispaused and the element is put into an open circuit state.

Still further, in Japanese Patent Application Laid-Open No. 2002-122843,there is disclosed a drive method for a light control element usingliquid crystal, in which a high voltage is applied to the light controlelement prior to normal drive so as to accelerate the operation of theliquid crystal element.

In order to control the light transmittance of the EC element, the PWMdrive for adjusting the duration (duty ratio) of voltage application forcausing the electrochemical reaction can be used. However, there hasbeen the following problem in a process of changing a magnitude of thelight transmittance. Specifically, the light transmittance depends onthe duty ratio, and hence in order to change the light transmittance, aset value of the duty ratio needs to be changed. The light transmittancechanges toward a value corresponding to the set duty ratio while passingthrough a transitional state, and is then saturated and maintained atthis value. At this time, when a length of time spent during thetransitional state is long, operating performance of the EC elementdeteriorates, and hence the transitional characteristics need to beimproved.

In Japanese Patent Application Laid-Open No. H11-109423 and in “SolarEnergy Materials & Solar Cells” 104, (2012), pp. 140 to 145, noconsideration is given to improvement of the transitionalcharacteristics in which the light transmittance changes, and thosedisclosures of the related art have been insufficient for theenhancement of the operating performance of the EC element.

Further, a method of applying a voltage higher than a normal voltageduring the transitional state to accelerate the element operation, suchas the drive of the liquid crystal element disclosed in Japanese PatentApplication Laid-Open No. 2002-122843, has not been necessarilypreferred for the EC element. For example, in an organic EC elementcontaining a plurality of types of materials, due to a difference inoxidation-reduction potential or molar absorption coefficient among thematerials, the absorption spectrum changes in some cases relative to avoltage. Therefore, there has been required a drive method that isparticularly preferred for the organic EC element.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedbackground art, and has an object to provide a method and apparatus fordriving an electrochromic element having an excellent operatingperformance, which are capable of controlling, during a transitionalstate in which a light transmittance changes, a speed and period of thetransitional state.

According to one embodiment of the present invention, there is providedan apparatus for driving an electrochromic element, the apparatus beingconfigured to apply a continuous drive pulse to an electrochromicelement, the electrochromic element including an electrochromic layerthat contains an electrochromic material and is sandwiched between apair of electrodes, and to change an absorbance of the electrochromicelement with use of a duty ratio of the continuous drive pulse,

the continuous drive pulse having one cycle including an applied periodof a drive voltage and a stopped period of the drive voltage,

the drive voltage being a voltage for causing at least one of anoxidation reaction of the electrochromic material and a reductionreaction of the electrochromic material, the stopped period being aperiod in which, in a closed circuit including the electrochromicelement, a resistor having a resistance value larger than a resistancevalue of another resistor to be connected during the applied period isconnected in series,

the duty ratio being a ratio of the applied period of the drive voltageto the one cycle,

the apparatus being configured to perform, when the absorbance of theelectrochromic element is to be increased from a current absorbance to atarget absorbance, before normal drive of driving the electrochromicelement at a duty ratio D1 for maintaining the target absorbance,accelerated drive of driving the electrochromic element at a duty ratioD2 larger than the duty ratio D1.

Further, according to one embodiment of the present invention, there isprovided a method of driving an electrochromic element, for applying acontinuous drive pulse to an electrochromic element, the electrochromicelement including an electrochromic layer that contains anelectrochromic material and is sandwiched between a pair of electrodes,and changing an absorbance of the electrochromic element with use of aduty ratio of the continuous drive pulse,

the continuous drive pulse having one cycle including an applied periodof a drive voltage and a stopped period of the drive voltage,

the drive voltage being a voltage for causing at least one of anoxidation reaction of the electrochromic material and a reductionreaction of the electrochromic material,

the stopped period being a period in which, in a closed circuitincluding the electrochromic element, a resistor having a resistancevalue larger than a resistance value of another resistor to be connectedduring the applied period is connected in series,

the duty ratio being a ratio of the applied period of the drive voltageto the one cycle,

the method including performing, when the absorbance of theelectrochromic element is to be increased from a current absorbance to atarget absorbance, before normal drive of driving the electrochromicelement at a duty ratio D1 for maintaining the target absorbance,accelerated drive of driving the electrochromic element at a duty ratioD2 larger than the duty ratio D1.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram for illustrating an example of an ECapparatus using a drive apparatus according to the present invention.

FIG. 2 is a schematic cross-sectional view for illustrating an exampleof an EC element to be used in the present invention.

FIG. 3 is a diagram for illustrating a voltage application methodaccording to the present invention.

FIG. 4 is a diagram for illustrating one drive control mode of a drivemethod according to the present invention.

FIG. 5 is a diagram for illustrating an example of an image pickupapparatus according to the present invention.

FIG. 6 is a diagram for illustrating another example of the image pickupapparatus according to the present invention.

FIG. 7A and FIG. 7B are views each for illustrating an example of awindow member according to the present invention.

FIG. 8 is a graph for showing a change in absorbance obtained when an ECelement according to Example of the present invention was driven from adecolored state at a fixed duty ratio in a coloring direction.

FIG. 9 is a graph for showing a change with time in absorbance of the ECelement according to Example 1 obtained when accelerated drive was used.

FIG. 10A, FIG. 10B, and FIG. 10C are graphs each for showing anabsorption spectrum of an EC element according to Example 2 of thepresent invention.

FIG. 11 is a graph for showing a relationship between a change inabsorbance and drive time of an EC element according to Example 3 of thepresent invention.

FIG. 12 is a graph for showing a change in absorbance of an EC elementaccording to Example 4 of the present invention in a decoloringdirection.

FIG. 13A, FIG. 13B, FIG. 13C, and FIG. 13D are graphs each for showing achange with time in absorbance of an EC element according to Example 5of the present invention at the time of coloring and decoloring.

DESCRIPTION OF THE EMBODIMENTS

Now, the present invention is described in detail.

<<Method and Apparatus for Driving EC Element>>

FIG. 1 is a schematic diagram for illustrating an example of an ECapparatus using a drive apparatus of the present invention. The ECapparatus of FIG. 1 includes an EC element 1 in which an EC layercontaining an EC material is sandwiched between a pair of electrodes,and a drive apparatus configured to drive the EC element 1 (a drivepower supply 8, a resistor switch 9, and a controller 10).

(EC Element)

FIG. 2 is a schematic cross-sectional view for illustrating an exampleof an EC element to be used in the present invention. The EC element ofFIG. 2 has a configuration in which transparent substrates 2 and 6having formed thereon transparent electrodes 3 and 5, respectively arebonded to each other through a spacer 4 so that electrode 3 and 5 sidesface each other, and an EC layer 7 in which an electrolyte and anorganic EC material are dissolved in a solvent is present in a spaceformed by the pair of electrodes 3 and 5 and the spacer 4. The organicEC material causes an electrochemical reaction when a voltage is appliedbetween the electrodes 3 and 5. Note that, the present invention ispreferably applied to an organic EC element, but may be applied to aninorganic EC element using an inorganic EC material.

In general, the organic EC material is in a neutral state under a statein which a voltage is not applied, and does not show absorption in avisible light region. In such decolored state, the organic EC elementexhibits a high light transmittance. When a voltage is applied betweenthe electrodes, the organic EC material causes an electrochemicalreaction to be converted from the neutral state to an oxidized state(cation) or a reduced state (anion). The organic EC material showsabsorption in the visible light region in the form of cation or anion,to be colored. In such colored state, the organic EC element exhibits alow light transmittance. In addition, there also exists a material thatforms a transparent dication structure in an initial state and iscolored in blue through one-electron reduction, like a viologen, whichis a typical organic EC material.

In the following discussion, the light transmittance of the EC elementis replaced with the absorbance of the EC element. The transmittance andthe absorbance have a relationship of −log (transmittance)=(absorbance).Every time the transmittance is reduced to ½, the absorbance isincreased by about 0.3.

<Substrates 2 and 6>

In the case of using the EC element as a light control element, it ispreferred that the EC element keep a high transmittance in a decoloredstate in order to reduce an influence on an optical system. Therefore,the substrates 2 and 6 are each preferably a transparent substrateconfigured to sufficiently transmit visible light. A grass material isgenerally used, and an optical glass substrate such as Corning #7059 orBK-7 may be preferably used. In addition, even a material such asplastic or ceramic may be appropriately used as long as the material hassufficient transparency. The substrates 2 and 6 are each preferablyformed of a rigid material with less distortion. In addition, thesubstrates each more preferably have less flexibility. In general, thesubstrates 2 and 6 each have a thickness of from several tens ofmicrometers to several millimeters.

<Electrodes 3 and 5>

In the case of using the EC element as a light control element, it ispreferred that the EC element keep a high transmittance in a decoloredstate in order to reduce an influence on an optical system. Therefore,the electrodes 3 and 5 are each preferably a transparent electrodeconfigured to sufficiently transmit visible light. The electrodes 3 and5 are each more preferably formed of a material having a high lighttransmitting property in a visible light region and highelectroconductivity. Examples of such material may include: metals andmetal oxides such as indium tin oxide alloy (ITO), tin oxide (NESA),indium zinc oxide (IZO), silver oxide, vanadium oxide, molybdenum oxide,gold, silver, platinum, copper, indium, and chromium; silicon-basedmaterials such as polycrystalline silicon and amorphous silicon; andcarbon materials such as carbon black, graphene, graphite, and glassycarbon. In addition, an electroconductive polymer having itselectroconductivity improved through, for example, doping treatment(such as polyaniline, polypyrrole, polythiophene, polyacetylene,polyparaphenylene, or a complex of polyethylene dioxythiophene andpolystyrene sulfonate (PEDOT:PSS)) may also suitably be used. The ECelement of the present invention preferably has a high transmittance ina decolored state, and hence, for example, ITO, IZO, NESA, PEDOT:PSS, orgraphene is particularly preferably used. These materials may be used invarious forms such as a bulk form and a fine particle form. Note that,one of these electrode materials may be used alone, or a pluralitythereof may be used in combination.

<EC Layer 7>

The EC layer 7 is preferably an EC layer in which an electrolyte and atleast one kind of organic EC material such as a low-molecular organicmaterial are dissolved in a solvent.

The solvent is not particularly limited as long as the solvent candissolve the electrolyte, but a polar solvent is particularly preferred.Specific examples thereof include water as well as organic polarsolvents such as methanol, ethanol, propylene carbonate, ethylenecarbonate, dimethyl sulfoxide, dimethoxyethane, acetonitrile,γ-butyrolactone, γ-valerolactone, sulfolane, dimethylformamide,dimethoxyethane, tetrahydrofuran, acetonitrile, propionitrile,dimethylacetamide, methylpyrrolidinone, and dioxolane.

The electrolyte is not particularly limited as long as the electrolyteis an ion dissociative salt exhibiting satisfactory solubility andincluding a cation or anion having an electron-donating property to theextent that the coloration of the organic EC material can be ensured.Examples thereof include various inorganic ion salts such as alkalimetal salts and alkaline earth metal salts, quaternary ammonium salts,and cyclic quaternary ammonium salts. Specific examples thereof include:salts of alkali metals such as Li, Na, and K, e.g., LiClO₄, LiSCN,LiBF₄, LiAsF₆, LiCF₃SO₃, LiPF₆, LiI, NaI, NaSCN, NaClO₄, NaBF₄, NaAsF₆,KSCN, and KCl; and quaternary ammonium salts and cyclic quaternaryammonium salts such as (CH₃)₄NBF₄, (C₂Hs)₄NBF₄, (n-C₄H₉)₄NBF₄,(C₂Hs)₄NBr, (C₂Hs)₄NClO₄, and (n-C₄H₉)₄NClO₄. In addition, an ionicliquid may also be used. One of these electrolyte materials may be usedalone, or a plurality thereof may be used in combination.

As the organic EC material, any material may be used as long as thematerial has solubility in the solvent and can express coloration anddecoloration through an electrochemical reaction. A known organic ECmaterial to be colored through oxidation/reduction may be used. Inaddition, a plurality of such materials may be used in combination. Thatis, the organic EC element according to an embodiment of the presentinvention may include a plurality of kinds of EC materials.

Regarding the combination of the organic EC material, there may be usedone kind or a plurality of kinds of anodic materials each showingcoloration through an oxidation reaction, or one kind or a plurality ofkinds of cathodic materials each showing coloration through a reductionreaction. In addition, the anodic material and the cathodic material maybe used as a combination of one kind each of these materials, acombination of one kind of one of the materials and a plurality of kindsof the other materials, or a combination of a plurality of kinds each ofthese materials. The combination is arbitrary.

Specific examples of the organic EC material to be used may include:organic dyes such as a viologen dye, a styryl dye, a fluoran dye, acyanine dye, and an aromatic amine dye; and organometallic complexessuch as a metal-bipyridyl complex and a metal-phthalocyanine complex.

Specific examples of the cathodic EC material include: viologen-basedcompounds such as N,N′-diheptylbipyridinium diperchlorate,N,N′-diethylbipyridinium dihexafluorophosphate,N,N′-dibenzylbipyridinium ditetrafluoroborate, N,N′-diphenylbipyridiniumdihexafluorophosphate; anthraquinone-based compounds such as2-ethylanthraquinone, 2-t-butylanthraquinone; ferrocenium salt-basedcompounds such as ferrocenium tetrafluoroborate, ferroceniumhexafluorophosphate; styryl-based compounds. But the cathodic ECmaterials to use for this invention are not things limited to these.

Specific examples of the anodic EC material include: thiophenederivatives; metallocene derivatives such as ferrocene; aromatic aminederivatives such as phenazine derivatives, triphenylamine derivatives,phenothiazine derivatives, phenoxazine derivatives; pyrrole derivatives;pyrazoline derivatives. But the anodic EC materials to use for thisinvention are not things limited to these.

Of those materials, a compound represented by the following generalformula [1] is preferred because generated cations do not causeassociation with each other. A composition in which a plurality of thecompounds each represented by the following general formula [1] aremixed is more preferred.

In the formula, B, B′, C, and C′ are each independently selected from analkyl group having 1 or more to 20 or less carbon atoms, an alkoxy grouphaving 1 or more to 20 or less carbon atoms, and an aryl group that mayhave a substituent.

R₁ represents a hydrogen atom or a substituent.

n represents an integer of from 1 to 5.

X represents a structure represented by the following general formula[2] or [3], and when n represents an integer of 2 or more, X's are eachindependently selected from the structures represented by the followinggeneral formulae [2] and [3].

In the formulae, R₂ and R₃ are each independently selected from ahydrogen atom, an alkyl group having 1 or more to 20 or less carbonatoms, an alkoxy group having 1 or more to 20 or less carbon atoms, anaryl group that may have a substituent, and an alkyl ester group having1 or more to 20 or less carbon atoms; and R₄ represents an alkylenegroup having 1 or more to 20 or less carbon atoms.

In addition, when a thiophene ring adjacent to an aromatic ring havingthe groups B, B′, C, and C′ in the general formula [1] is represented bythe general formula [2], R₂ and R₃ each represent a substituent otherthan a hydrogen atom.

Examples of the substituent that the aryl group represented by any oneof B, B′, C, and C′ may have include an alkyl group having 1 or more to4 or less carbon atoms and an alkoxy group having 1 or more to 4 or lesscarbon atoms. In addition, examples of the substituent represented by R₁include a halogen atom, an alkyl group having 1 or more to 20 or lesscarbon atoms, an alkoxy group having 1 or more to 20 or less carbonatoms, an alkyl ester group having 1 or more to 20 or less carbon atoms,an aryl group that may have a substituent, an amino group that may havea substituent, and a cyano group, and the aryl group and the amino groupmay each have as a substituent an alkyl group having 1 or more to 4 orless carbon atoms. In addition, examples of the substituent that thearyl group represented by R₂ or R₃ may have include an alkyl grouphaving 1 or more to 4 or less carbon atoms and an alkoxy group having 1or more to 4 or less carbon atoms.

Specific examples of the compound represented by the general formula [1]include the following compounds 1 to 3.

The compound represented by the general formula [1] includes: a portionX exhibiting EC characteristics and having a structure including athiophene ring; and aromatic rings each having substituents at positions2 and 6 (B and C, and B′ and C′) on terminal portions of the structurerepresented by X. Of thiophene rings in the structure represented by X,a thiophene ring adjacent to each aromatic ring on the terminal portionhas at positions 3 and 4 the substituents (R₂ and R₃) other than ahydrogen atom, such as the alkyl group, or has at these positions thealkylene dioxy group (R₄).

The plane of each aromatic ring on the terminal portion is twisted withrespect to the plane of the thiophene ring in the structure representedby X through steric hindrance between the substituents of the aromaticring on the terminal portion and the substituents at positions 3 and 4of the thiophene ring adjacent to the aromatic ring on the terminalportion. A driving force for causing association is considered to be π-πinteraction between a thiophene molecule and another thiophene moleculeeach exhibiting EC characteristics and forming radical cations. Asdescribed above, the aromatic ring on the terminal portion has amolecular structure twisted with respect to the plane of the thiophenering, and hence the thiophene ring is prevented from being close toanother thiophene ring of another organic EC molecule through the sterichindrance with the aromatic ring on the terminal portion and itssubstituents B and C, or B′ and C′. Thus, association is not caused.

In the investigations made by the inventors of the present invention,association is not visually observed to be formed in the compoundrepresented by the general formula [1]. A material that causesassociation shows different behavior of absorption change betweencations and cations in an associated form at the time of coloring anddecoloring. As a result, an absorption spectrum largely changes in somecases. However, the light transmittance of the compound represented bythe general formula [1] can be controlled in both a coloring directionand a decoloring direction while the shape of the absorption spectrum ismaintained. Note that, even the material that causes association may bemixed with the compound represented by the general formula [1] whenabsorption shown by the material in an associated form in itself is notso high as to be visually observed, and does not affect the absorptionspectrum.

The EC layer 7 may be an EC layer in which an inorganic EC material isdispersed in a solution. Examples of the inorganic EC material mayinclude tungsten oxide, vanadium oxide, molybdenum oxide, iridium oxide,nickel oxide, manganese oxide, and titanium oxide.

The EC layer 7 is preferably a liquid or a gel. The EC layer 7 issuitably used in a solution state, but may also be used in a gel state.Gelling is carried out by further incorporating a polymer or a gellingagent into a solution. Examples of the polymer (gelling agent) include,but not particularly limited to, polyacrylonitrile,carboxymethylcellulose, polyvinyl chloride, polyvinyl bromide,polyethylene oxide, polypropylene oxide, polyurethane, polyacrylate,polymethacrylate, polyamide, polyacrylamide, polyester, polyvinylidenefluoride, and Nafion. Thus, the EC layer 7 may be used in a viscousstate, a gel state, or the like.

In addition, the EC layer may be used in a state in which the solutionis supported by a structural body having a transparent and flexiblenetwork structure (for example, a sponge-like one), other than in themixed state as described above.

(Drive Apparatus and Drive Method)

In FIG. 1, the drive apparatus includes the drive power supply 8, theresistor switch 9, and the controller 10. The drive apparatus applies acontinuous drive pulse to the EC element 1, and uses a duty ratio of thedrive pulse to change the absorbance of the EC element.

The drive power supply 8 applies, to the EC element 1, a voltage (drivevoltage V1) for causing at least one of the oxidation reaction andreduction reaction of the EC material. When the EC layer 7 contains onetype of EC material, the value of V1 may be changed substantially withinsuch a range as to cause a normal electrochemical reaction. On the otherhand, when the EC layer 7 contains a plurality of types of EC materials,it is preferred that V1 be a constant voltage because an absorptionspectrum may change due to a difference in oxidation-reduction potentialor molar absorption coefficient among the EC materials. In view of bothof the cases, it is more preferred that the drive voltage V1 be aconstant voltage. The voltage application of the drive power supply 8 isstarted based on a signal of the controller 10, and a state in which thevoltage is applied is maintained based also on the signal of thecontroller 10. In the present invention, during a period in which thelight transmittance of the EC element 1 is controlled, the state inwhich the constant voltage is applied is maintained.

The resistor switch 9 switches a resistor R1, which is to be connectedduring an applied period, and a resistor R2, which has a resistancevalue larger than that of the resistor R1, from one to another, andconnects the selected one of the resistors in series to a closed circuitincluding the drive power supply 8 and the EC element 1. It is preferredthat a resistance value of the resistor R1 be smaller than at least thelargest impedance in the element closed circuit, and the resistancevalue is preferably 10Ω or smaller. It is preferred that the resistancevalue of the resistor R2 be larger than the largest impedance in theelement closed circuit, and the resistance value is preferably 1 MΩ orlarger. Further, the resistor R2 may be assumed to be air. In this case,the closed circuit is an open circuit in a strict sense, but when theair is assumed as the resistor R2, the open circuit is equivalent to theclosed circuit.

The controller 10 sends a switch signal to the resistor switch 9 tocontrol the switching between the resistor R1 and the resistor R2.

FIG. 3 is a diagram for illustrating a voltage application methodaccording to the present invention. A drive pulse illustrated in FIG. 3has one cycle T including an applied period t_(on) of the drive voltageV1 and a stopped period t_(off) thereof. The stopped period t_(off) is aperiod in which in the closed circuit including the EC element 1, theresistor R2, which has the resistance value larger than that of theresistor R1 to be connected during the applied period t_(on), isconnected in series. In addition, the duty ratio is a ratio of theapplied period t_(on) of the drive voltage V1 to the one cycle.

A condition necessary to maintain a written state of the EC element 1through the duty drive is that a current is caused to flow through anexternal circuit during the applied period t_(on) of the drive voltageV1 but the current is not caused to flow through the external circuitduring the stopped period t_(off). The EC element 1 has such acharacteristic that when a forward current is caused to flow, thecurrent causes a reaction and the EC element 1 is thus colored, but whenthe current is caused to flow in a reverse direction, a reverse reactionis caused and the EC element 1 is thus decolored. Considering this, whena potential difference between the electrodes is decreased during thestopped period t_(off), a sudden decoloring reaction occurs, and thewritten state cannot be maintained as a result. However, by insertingthe resistor to the external circuit portion of the EC element 1 inseries during the stopped period t_(off), it is possible to suppress thecurrent flowing through the external circuit. In this manner, it ispossible to suppress a sudden decoloring reaction, to thereby maintainthe written state. Under the state in which the resistor is inserted tothe external circuit in series, only a current generated by diffusion ofthe EC molecules between the electrodes flows between the electrodes,and hence an amount of current generated by a reverse reaction is small,which reduces a fluctuation of the written state. Therefore, a fixedabsorbance can be maintained by applying a certain duty ratio. In otherwords, the stopped period t_(off) as used herein does not mean a periodin which the voltage is not applied, but means a period in which thecurrent is not caused to flow through the external circuit of the ECelement 1 and the potential difference between the electrodes is notattenuated actively. Accordingly, even if the resistance value of theexternal resistor R2 inserted during the stopped period t_(off) issignificantly large and the potential difference between the electrodesis the same during both of the applied period t_(on) and the stoppedperiod t_(off) of the drive voltage V1, the voltage is appliedcontinuously but the current is not caused to flow. Therefore, theoxidation or reduction reaction of the EC material does not occur. Thus,during the stopped period t_(off), only a gradual reverse reactionoccurs, and a sudden change in light amount does not occur. This pointgreatly differs in principle from a liquid crystal element, which isdriven based on an effective voltage value and, even if a current doesnot flow through the element, makes an electrochemical response when avoltage is applied to the element. Therefore, a written amount of theliquid crystal element cannot be controlled based on such a drive methodas described in the present invention.

More specifically, in FIG. 3, from a starting point of drive, the drivepower supply 8 applies, to the EC element 1, the voltage (drive voltageV1) for causing at least one of the oxidation reaction or reductionreaction of the EC material. When receiving the signal from thecontroller 10, the resistor switch 9 switches the resistor R1 and theresistor R2 from one to another, and connects the selected one of theresistors to the closed circuit including the EC element 1 and the drivepower supply 8. When the resistor switch 9 switches a state of wiringconnection between a connected state and a disconnected state asillustrated in FIG. 1, the circuit state is switched between the closedcircuit state and the open circuit state based on the operation of theresistor switch 9 as illustrated in FIG. 3. The closed circuit state isa voltage applied state, and the open circuit state is a state in whichthe resistor R2 is inserted to the power supply in series (this state ishereinafter referred to as “stopped state”). In the voltage appliedstate, the EC element 1 exhibits a coloring reaction. In the stoppedstate, the EC element 1 exhibits a “self-decoloring phenomenon”, inwhich the colored material is decolored. The self-decoloring phenomenonis caused by, for example, instability of the cation or anion of the ECmaterial generated by the electrochemical reaction, or diffusion of thecation or the anion to a counter electrode having a different potential.When a certain duty ratio is given, the absorbance changes until abalance is reached between a colored amount and a self-decoloringamount, and then the balanced absorbance is maintained. The magnitude ofthe absorbance can be controlled through the application and stop ofsuch a pulse drive of the drive voltage V1, namely, through anintermittent drive of the drive voltage V1, because the EC element, inparticular, the organic EC element, has the self-decoloring phenomenon.Accordingly, it follows that the above-mentioned drive method is amethod suitable for the organic EC element. Note that, the drive voltageV1 is supplied during both of the applied period and the stopped periodwithout changing its value.

The switching between the voltage application and the stop of voltageapplication is controlled by the controller 10, and the controller 10sends, to the resistor switch 9, the continuous pulse having the onecycle T corresponding to a sum of the applied period t_(on) and thestopped period t_(off). Now, the ratio of the applied period t_(on) tothe one cycle T is defined as the duty ratio. When the EC element 1 isdriven at a fixed duty ratio under the constant voltage of the drivepower supply 8 as illustrated in FIG. 3, a change in absorbance issaturated after passing through the transitional state, and then thesaturated absorbance is maintained. In order to decrease the absorbance,it is only necessary that the duty ratio be fixed to the one smallerthan the last duty ratio. Further, in order to increase the absorbance,it is only necessary that the duty ratio be fixed to the one larger thanthe last duty ratio.

The controller 10 has a characteristic table about a duty ratio and theabsorbance to be reached with the duty ratio for at least each of thecoloring direction and the decoloring direction, namely, has at leasttwo such characteristic tables. In normal drive, the controller 10selects a duty ratio D1, which is required for the absorbance to reach atarget absorbance. When the one cycle T of the control signal is long,an increase or decrease of an absorbance change is viewable in somecases, and hence an upper limit of the one cycle T is at least 100milliseconds or shorter, preferably 10 milliseconds or shorter. Further,a lower limit of the one cycle T is determined so that the lower limitfalls within such a range as to enable the electrochemical reaction tofollow the cycle, and the lower limit is 1 microsecond or longer,preferably 10 microseconds or longer. It is preferred that the one cycleT be fixed, but a certain deviation within the above-mentioned range istolerated in some cases.

FIG. 4 is a diagram for illustrating one drive control mode of the drivemethod according to the present invention.

As illustrated in FIG. 4, in the present invention, when the absorbanceof the EC element 1 is to be increased from a current absorbance to thetarget absorbance, accelerated drive is performed immediately beforenormal drive under the state in which the drive voltage V1 is applied.In this case, the normal drive is drive performed at the duty ratio D1to maintain the target absorbance, and the accelerated drive is driveperformed at a duty ratio D2, which is larger than the duty ratio D1. Inthis manner, a length of time spent for the transitional state in thecoloring direction can be shortened, with the result that the operatingperformance of the EC element 1 can be enhanced. In this case, it ispreferred that the duty ratio D2 be 100%, which enhances theacceleration most.

Further, when the absorbance of the EC element 1 is to be decreased froma current absorbance to a target absorbance, it is preferred thataccelerated drive be performed immediately before normal drive under thestate in which the drive voltage V1 is applied. In this case, the normaldrive is drive performed at a duty ratio D3 to maintain the targetabsorbance, and the accelerated drive is drive performed at a duty ratioD4, which is smaller than the duty ratio D3. In this manner, a length oftime spent for the transitional state in the decoloring direction can beshortened, with the result that the operating performance of the ECelement 1 can be enhanced. In this case, it is preferred that the dutyratio D4 be 0%, which enhances the acceleration most.

In this case, the process in which the duty ratio is 0% is a process ofinserting the resistor to the external circuit without changing thepower supply voltage, thereby causing the EC element to be decoloredthrough the self-decoloring without causing the electrode reaction ofthe EC material. However, only at the time of decoloring, it is alsopossible to feed the electric power at such a potential as to cause theoxidation or reduction or less (e.g., 0 V), and not to connect theresistor to the external circuit. Note that, when there is one drivepower supply, the drive power supply does not necessarily supply poweronly to the organic EC element, but supplies the power also to thecontroller, the resistor switch, and other peripheral devices. In such asystem, it is not preferred to change the drive power supply itself, andit is desired that as in the present invention, the duty ratio becontrolled under the state in which the power from the drive powersupply is being supplied.

A method of applying a voltage higher than a normal voltage during thetransitional state to accelerate the element operation, such as anoverdrive technology for liquid crystal, is not necessarily preferredin, for example, the organic EC element containing the plurality oftypes of EC materials. This is because due to a difference inoxidation-reduction potential or molar absorption coefficient among theEC materials, the absorption spectrum changes relative to the voltage insome cases.

Further, through the use of the method and apparatus for driving anorganic EC element according to the present invention, it is possible todefine a period of the accelerated drive in the accelerated drive in thecoloring direction.

In general, the speed of an electrode reaction of an organic material isaffected by a charge-transfer process between a reactant and anelectrode and a mass transfer process in which a reactant is supplied toan electrode interface. When an overvoltage enough to cause theelectrochemical reaction of the organic material is applied to theelectrode, the charge-transfer process has a time constant on the orderof microseconds, and is a process that progresses overwhelmingly fasterthan the mass transfer process. Therefore, the electrode reaction israte-controlled by the mass transfer process. Further, when the organicEC element is placed under a stationary environment, the mass transferis determined based mainly on diffusion of a material.

In the field of electrochemistry, it is known that a change with time indiffusion current under a constant potential follows a Cottrell equationof Formula (1).

$\begin{matrix}{{i(t)} = {\frac{{zFD}_{0}C_{0}}{\sqrt{\pi \; D_{0}}}\frac{1}{\sqrt{t}}}} & (1)\end{matrix}$

In Formula (1), i(t) represents the diffusion current under the constantpotential, z represents the number of reaction electric charges, Frepresents the Faraday constant, D₀ represents a diffusion coefficientof an organic material before reaction, and C₀ represents aconcentration of the organic material before reaction in the bulkseparated from the electrode interface.

Further, an amount of change in absorbance in the coloring direction isrepresented by a Lambert-Beer equation of Formula (2).

ΔAbs=ε·ΔC(t)·L  (2)

In Formula (2), ΔAbs represents the amount of change in absorbance, εrepresents a molar absorption coefficient of an organic material afterreaction, ΔC(t) represents an amount of change in concentration of theorganic material after reaction, and L represents an optical pathlength. In this case, ΔC(t) is proportional to a current amount, andhence ΔC(t) is proportional to a time integral of i(t) of Formula (1),and a relationship of Formula (3) is established.

$\begin{matrix}{{\Delta \; {C(t)}} = {{k{\int{{i(t)}{t}}}} = {2k^{\prime}{zFC}_{0}\sqrt{\frac{D_{0}}{\pi}}\sqrt{t}}}} & (3)\end{matrix}$

In Formula (3), k and k′ represent proportionality constants.

Considering this, it can be understood that in the drive in the coloringdirection, a square (ΔAbs)² of a change in absorbance is proportional toa drive time t.

Note that, in the drive method of the present invention, the one cycleof the continuous pulse includes the voltage stopped period, and hencediffusion limitation of a material tends to be alleviated. However, thedrive method still includes the relationship of the diffusion limitationin the case of the above-mentioned period of time of the one cycle ofthe continuous pulse. Therefore, the proportional relationship between(ΔAbs)² and the drive time t is established.

Considering this, by applying the proportional relationship between(ΔAbs)² and t to the accelerated drive in the coloring direction, aperiod required for the accelerated drive can be calculated based on anamount of change between the current absorbance and the targetabsorbance.

Now, when arbitrary two absorbance change amounts in the accelerateddrive are represented by ΔQ_(m) and ΔQ_(n), and periods of theaccelerated drive that are required for the arbitrary two absorbancechange amounts ΔQ_(m) and ΔQ_(n), are represented by T_(m) and T_(n),respectively, from the proportional relationship between (ΔAbs)² and t,ΔQm²/Tm=ΔQn²/Tn is established. Therefore, a relationship of Formula (4)is established.

$\begin{matrix}{T_{m} = {\left( \frac{\Delta \; Q_{m}}{\Delta \; Q_{n}} \right)^{2}T_{n}}} & (4)\end{matrix}$

If T_(m), which is the period of the accelerated drive, is set as shownin Formula (5), drive that causes an absorbance change amount exceedinga necessary amount is performed as a result. In other words, theaccelerated drive is performed even after the target absorbance isreached.

$\begin{matrix}{T_{m} > {\left( \frac{\Delta \; Q_{m}}{\Delta \; Q_{n}} \right)^{2}T_{n}}} & (5)\end{matrix}$

In this case, the absorbance temporarily becomes larger than the targetabsorbance, and decreases a little during the process of the subsequentnormal drive. Then, the absorbance is saturated at the targetabsorbance. This is not preferred because in addition to a time loss, anunnecessary rebound of the absorbance is caused. Therefore, it ispreferred that T_(m), which is the period of the accelerated drive, becontrolled under a relationship of Formula (a).

$\begin{matrix}{T_{m} \leq {\left( \frac{\Delta \; Q_{m}}{\Delta \; Q_{n}} \right)^{2}T_{n}}} & (6)\end{matrix}$

In Formula (a), under a relationship of Tm<(Right Term), the accelerateddrive ends before the absorbance reaches the target absorbance, and theabsorbance increases a little during the process of the subsequentnormal drive. Then, the absorbance is saturated at the targetabsorbance. This case is preferred as compared with the case of Formula(5) because there is no rebound of the absorbance.

Further, the control of the period of the transitional state can also beachieved as follows. Specifically, (ΔQ)²/t is acquired in advance.(ΔQ)²/t is a slope of a line that is obtained by linearly approximatinga relationship between a square of an absorbance change amount ΔQ andthe time t of acceleration at the time of the accelerated drive. Then,when the absorbance of the EC element 1 is to be increased from thecurrent absorbance to the target absorbance, a drive time t₁corresponding to a change amount of the absorbance is calculated basedon the slope (ΔQ)²/t, and a period t₀ of the accelerated drive is set soas to satisfy t_(A)≦t₁.

In this example, the period of the accelerated drive is set based on thedifference between the magnitudes of the current absorbance and thetarget absorbance. A value of the current absorbance may be any value.Further, in a drive method in which when the absorbance is to bechanged, the EC element is always returned to the initial state (resetstate) and then controlled to be the target absorbance, the initialstate can be set as a reference. Therefore, this drive method has anadvantage in that time setting is facilitated more, and is applicabledepending on a mode of use.

<<Optical Filter>>

An optical filter according to the present invention includes an ECelement and the above-mentioned apparatus for driving the EC elementaccording to the present invention. Specifically, the optical filter is,for example, an example in which the EC apparatus illustrated in FIG. 1is applied as the optical filter, and the optical filter may include aperipheral device. The optical filter may be used in an image pickupapparatus such as a camera. When used in the image pickup apparatus, theoptical filter may be arranged in a main body of the image pickupapparatus, or may be arranged in a lens unit. Now, a case is describedwhere a neutral density (ND) filter is formed as the optical filter.

The neutral density filter absorbs black, and needs uniform lightabsorption in a visible light region. In order to realize the blackabsorption with the use of the organic EC material, it is only necessarythat a plurality of materials having different absorption regions in thevisible light region be mixed to make absorption flat in the visiblelight region. The absorption spectrum in the case of mixing the organicEC materials is expressed by a sum of the absorption spectra of therespective materials, and hence the black absorption can be realized byselecting a plurality of materials having appropriate wavelength regionsand adjusting concentrations thereof. What is important in this case isthat none of the organic EC materials causes association or that theorganic EC element is formed only of materials that do not have asignificant influence even when causing association.

An example of driving the neutral density (ND) filter according to thepresent invention is described below. In general, the neutral density(ND) filter reduces an amount of light to ½^(n) (where n is an integer).When the amount of light is reduced to ½, the transmittance is reducedfrom 100% to 50%. When the amount of light is reduced to ¼, thetransmittance is reduced from 100% to 25%. Further, when thetransmittance is reduced to ½, from a relationship of−LOG(transmittance)=(absorbance), the absorbance change amount is 0.3,and when the transmittance is reduced to ¼, the absorbance change amountis 0.6. In order to reduce the light amount so that the transmittancevaries from ½ to 1/64, it is only necessary that the absorbance changeamount be controlled to be from 0 to 1.8 in units of 0.3.

When the EC layer is in a solution state, the absorbance change amountincludes a change amount of the colored amount that is caused by afluctuation of the solution. In order to achieve accurate control, theoptical filter may be equipped with an external monitor configured tomeasure a light amount as a part of the optical filter.

<<Image Pickup Apparatus and Lens Unit>>

An image pickup apparatus according to the present invention includesthe above-mentioned optical filter according to the present inventionand a light receiving element configured to receive light that has beentransmitted through the optical filter.

Further, a lens unit according to the present invention includes theabove-mentioned optical filter according to the present invention and anoptical system including a plurality of lenses. The optical filter maybe arranged so that the light that has been transmitted through theoptical filter is then transmitted through the optical system.Alternatively, the optical filter may be arranged so that the light thathas been transmitted through the optical system is then transmittedthrough the optical filter.

FIG. 5 is a schematic diagram for illustrating the image pickupapparatus including the lens unit using the optical filter according tothe present invention. As illustrated in FIG. 5, a lens unit 102 isremovably connected to an image pickup apparatus 103 through a mountmember (not shown).

The lens unit 102 is a unit including a plurality of lenses or lensgroups. For example, the lens unit 102 illustrated in FIG. 5 is arear-focus zoom lens configured to perform focusing behind a diaphragm.The lens unit 102 includes, in order from a subject side (left side ofthe drawing), four lens groups of a first lens group 104 having apositive refractive power, a second lens group 105 having a negativerefractive power, a third lens group 106 having a positive refractivepower, and a fourth lens group 107 having a positive refractive power.An interval between the second lens group 105 and the third lens group106 is changed to vary magnification, and a part of lenses of the fourthlens group 107 is moved to perform focusing. For example, the lens unit102 includes a diaphragm 108 arranged between the second lens group 105and the third lens group 106, and further includes an optical filter 101arranged between the third lens group 106 and the fourth lens group 107.Those components are arranged so that the light to be transmittedthrough the lens unit 102 is transmitted through the lens groups 104 to107, the diaphragm 108, and the optical filter 101, and the amount oflight can be adjusted with the use of the diaphragm 108 and the opticalfilter 101.

Further, a configuration of the components of the lens unit 102 can bemodified appropriately. For example, the optical filter 101 may bearranged in front of the diaphragm 108 (on the subject side thereof), ormay be arranged behind the diaphragm 108 (on the image pickup apparatus103 side thereof). Alternatively, the optical filter 101 may be arrangedin front of the first lens group 104, or may be arranged behind thefourth lens group 107. When the optical filter 101 is arranged at aposition where light converges, there is an advantage in that an area ofthe optical filter 101 can be reduced, for example. Further, a mode ofthe lens unit 102 can also be selected appropriately. Instead of therear-focus zoom lens, the lens unit 102 may also be an inner-focus zoomlens configured to perform focusing in front of the diaphragm, or may beanother type of zoom lens configured to perform focusing in another way.Further, instead of the zoom lens, a special-purpose lens such as afisheye lens or a macro lens can also be selected appropriately.

A glass block 109 of the image pickup apparatus is a glass block such asa low-pass filter, a face plate, or a color filter. Further, a lightreceiving element 110 is a sensor unit configured to receive light thathas been transmitted through the lens unit 102, and an image pickupelement such as a CCD or a CMOS may be used as the light receivingelement 110. Further, the light receiving element 110 may also be anoptical sensor such as a photodiode, and a device configured to acquireand output information on intensity or wavelength of light can be usedappropriately as the light receiving element 110.

When the optical filter 101 is built into the lens unit 102 asillustrated in FIG. 5, the drive apparatus may be arranged within thelens unit 102, or may be arranged outside the lens unit 102. When thedrive apparatus is arranged outside the lens unit 102, the EC elementand the drive apparatus, which are respectively arranged within andoutside the lens unit 102, are connected to each other through wiring,and the drive apparatus drives and controls the EC element.

As illustrated in FIG. 6, the image pickup apparatus 103 itself mayinclude the optical filter 101 according to the present invention. FIG.6 is a schematic diagram of the image pickup apparatus including theoptical filter. The optical filter 101 is arranged at an appropriateposition within the image pickup apparatus 103, and it is only necessarythat the light receiving element 110 be arranged so as to receive thelight that has been transmitted through the optical filter 101. In FIG.6, for example, the optical filter 101 is arranged immediately in frontof the light receiving element 110. When the image pickup apparatus 103itself has the optical filter 101 built therein, the lens unit 102itself connected to the image pickup apparatus 103 does not need toinclude the optical filter 101, and hence it is possible to form theimage pickup apparatus using an existing lens unit and being capable ofcontrolling light.

The image pickup apparatus described above is applicable to a producthaving a combination of a function of adjusting a light amount and alight receiving element. The image pickup apparatus can be used in, forexample, a camera, a digital camera, a video camera, or a digital videocamera. The image pickup apparatus is also applicable to a producthaving the image pickup apparatus built therein, such as a mobile phone,a smartphone, a PC, or a tablet computer.

Through the use of the optical filter according to the present inventionas a light control member, it is possible to appropriately vary a lightamount to be controlled with the use of one filter, and there is anadvantage in that the number of members can be reduced and that a spacecan be saved, for example.

<<Window Member>>

A window member according to the present invention includes an ECelement and the above-mentioned apparatus for driving the EC elementaccording to the present invention. FIG. 7A and FIG. 7B are views eachfor illustrating the window member according to the present invention.FIG. 7A is a perspective view of the window member, and FIG. 7B is across-sectional view taken along the line 7B-7B of FIG. 7A.

The window member 111 of FIG. 7A and FIG. 7B is a light control window,and includes the EC element 1, transparent plates 113 for sandwichingthe EC element 1 therebetween, and a frame 112 for surrounding theentire window member to integrate those components into one windowmember. The drive apparatus may be built into the frame 112, or may bearranged outside the frame 112 and connected to the EC element 1 throughwiring.

The transparent plates 113 are not particularly limited as long as beingmade of a material having a high light transmittance. Considering theuse of the window member 111 as a window, it is preferred that thetransparent plates 113 be made of glass materials. In FIG. 7A and FIG.7B, the EC element 1 is a constituent member independent of thetransparent plates 113, but for example, the substrates 2 and 6 of theEC element 1 may be regarded as the transparent plates 113.

A material property of the frame 112 is not limited, but any member thatcovers at least a part of the EC element 1 and has a form of beingintegrated into one frame may be regarded as the frame.

The light control window described above is applicable to, for example,use of adjusting an amount of sunlight entering a room during thedaytime. The light control window can be used to adjust not only theamount of sunlight but also a heat quantity, and hence can be used tocontrol brightness and temperature of the room. Further, the lightcontrol window is also applicable to use as a shutter to prevent anindoor view from being seen from the outside of the room. The lightcontrol window described above is applicable not only to a glass windowfor a construction, but also to a window of a vehicle such as anautomobile, a train, an airplane, or a ship, and to a filter of adisplay surface of a clock, a watch, or a mobile phone.

Example 1

In Example 1, the drive apparatus illustrated in FIG. 1 was produced byusing as the organic EC material the compound 1, which formed cationsfrom neutral species through an oxidation reaction to be colored.

The EC element 1 had a construction as illustrated in FIG. 2. Two glassFTO substrates (substrates in which the electrodes 3 and 5 each formedof a fluorine-doped tin oxide thin film were formed on the substrates 2and 6 each made of glass) were bonded to each other through the spacer 4of 125 μm. The EC layer 7 was present in a space formed by thesubstrates 2 and 6 and the spacer 4. As the EC layer 7, a solutionobtained by dissolving the compound 1 in a propylene carbonate solventtogether with a supporting electrolyte (TBAP) was injected. Theconcentrations of the compound 1 and TBAP were 10 mM and 0.1 M,respectively. When a voltage of 2 V was applied between the electrodesas the drive voltage V1, the compound 1 was oxidized by the electrode onone side (anode) to be colored.

The drive power supply 8 applies the drive voltage V1. Connectionbetween the EC element 1 and the drive power supply 8 was controlled bya switch circuit (relay circuit) serving as the resistor switch 9, andthe switch circuit switched the state of wiring connection between thedrive power supply 8 and the EC element 1 between the connected stateand the disconnected state. Timing for controlling the switch circuitwas controlled based on voltage supply from an arbitrary waveformgenerator. The arbitrary waveform generator can be considered ascorresponding to a part of functions of the controller 10. The operationof the switch circuit was the same as connecting one of thelow-resistance resistor R1 and the high-resistance resistor R2 to wiringof the EC element 1 in series. In this case, the low-resistance resistorR1 can be regarded as a resistor of a wiring material, and had aresistance value of 10Ω or smaller. Further, the high-resistanceresistor R2 was the air, and hence its resistance value far exceeded 1MΩ.

An amount of current flowing through the circuit was controlled byswitching the resistor to be connected to the element circuit betweenthe low-resistance resistor R1 and the high-resistance resistor R2 inthis manner. When the element circuit was connected to thelow-resistance resistor R1, the current flowed to cause the oxidationreaction. As a result, the EC element was colored. When the elementcircuit was connected to the high-resistance resistor R2, no currentflowed, and hence the oxidation reaction was not caused. At this time,the organic EC element exhibited the self-decoloring phenomenon due todiffusion. Until the balance was reached between the oxidation reactionamount and the self-decoloring amount, the absorbance changedtransiently, and after the balance was reached, the balanced absorbancewas maintained.

The change of absorbance was measured with the use of a spectrometer(manufactured by Ocean Optics, Inc., USB2000+) capable of measuringabsorption in ultraviolet, visible, and near infrared wavelengthregions. In the following, unless otherwise noted, the magnitude of theabsorbance means an absorbance at a single wavelength corresponding toany one of absorption peaks exhibited by the EC element 1.

FIG. 8 is a graph for showing a change in absorbance (change exhibitedby the compound 1 at the absorption peak at 600 nm) obtained when the ECelement was driven at a fixed duty ratio in the coloring direction whileassuming the initial state in which the EC element is decolored as astarting point.

As shown in FIG. 8, when the application of the drive voltage V1 and thecontrol at the fixed duty ratio were performed at the same time on theEC element while assuming a state in which the EC element is not coloredas the initial state, the EC element changed its magnitude of theabsorbance to be reached depending on the magnitude of the duty ratio.Thus, the light transmittance was able to be controlled based on thecontrol of the duty ratio. Further, as the duty ratio became larger, anamount and speed of change in absorbance became larger, and the timespent for the transitional state became shorter.

From this result, by performing the accelerated drive at the duty ratioD2 larger than the duty ratio D1 before the normal drive at the dutyratio D1 for causing the absorbance to reach the target absorbance andmaintaining the target absorbance, it is possible to enhance theoperating performance in the coloring direction.

FIG. 9 is a graph for showing a change with time in absorbance of the ECelement obtained when the accelerated drive was used. In FIG. 9, a line“(a)” indicates a change with time in absorbance obtained when the dutyratio D2 was set to 100% in the accelerated drive and the duty ratio D1was set to 2% in the subsequent normal drive. Timing for controlling theduty ratio is indicated by a line “(c)”. On the other hand, a line “(b)”indicates a change with time in absorbance obtained when the normaldrive was performed at the duty ratio of 4% from the initial statewithout performing the accelerated drive. It is revealed that, ascompared with the case of the line “(b)”, time spent for thetransitional state was significantly reduced in the case of the line“(a)”, and it is clear that the accelerated drive is highly effective.

Example 2

In Example 2, a plurality of kinds of materials that formed cations fromneutral species through an oxidation reaction to be colored were mixedto be used as the organic EC material. The materials used were thecompounds 1 to 3 described above and the following compound 4. Theconcentrations of the compounds 1 to 4 were 13 mM, 30 mM, 8 mM, and 2mM, respectively, and other element constructions were the same as inExample 1.

FIG. 10A to FIG. 10C are graphs each for showing an absorption spectrumat the time of driving of the organic EC element.

FIG. 10A is a graph for showing a change in absorption spectrum in acoloring direction at the time of application of a constant voltage of2.0 V for 3 seconds. Arbitrary four time points were extracted andsuperposed in one graph. The materials simultaneously reacted, and thecompound 1 shows absorption at 540 nm and 600 nm, the compound 2 showsabsorption at 440 nm and 490 nm, the compound 3 shows absorption at 500nm and 630 nm, and the compound 4 shows absorption at 500 nm and 530 nm.

FIG. 10B is a graph in which the absorption spectra at the respectivetime points shown in FIG. 10A were normalized with reference to 630 nmand superposed on each other. From the fact that the spectraapproximately coincide with each other, it is revealed that theabsorbance can be changed without changing the absorption spectrum inthe case of driving at a constant voltage.

On the other hand, FIG. 10C is a graph in which the absorption spectraat the drive voltages of 2.2 V, 2.4 V, and 2.6 V were normalized withreference to 630 nm and superposed on each other. It is revealed fromFIG. 10C that when the drive voltage is changed, the absorption spectrumchanges significantly. This was conceivably caused by the difference inoxidation-reduction potential or molar absorption coefficient among thematerials.

From this result, it is revealed that when the EC element is the organicEC element, in particular, the organic EC element containing a pluralityof types of EC materials, it is preferred that the drive voltage be aconstant voltage. Further, by performing the accelerated drive at theduty ratio D2 larger than the duty ratio D1 under the constant drivevoltage before the normal drive at the duty ratio D1 for maintaining thetarget absorbance, it is possible to enhance the operating performancein the coloring direction while maintaining the absorption spectrum.

Example 3

In Example 3, as the EC layer 7, a solution obtained by dissolving thecompound 4 and 1,1′-diethyl-4,4′-bipyridinium dichloride (ethylviologen) in a propylene carbonate solvent together with a supportingelectrolyte (TBAP) was injected. The concentrations of the compound 4and ethyl viologen were 10 mM and 10 mM, respectively, and other elementconstructions were the same as in Example 1. Note that, ethyl viologenhad a dication structure of a quaternary ammonium salt of4,4′-bipyridine. When a voltage was applied, a one-electron reductionreaction occurred, and the EC layer changed to blue from transparent.Further, when a reverse voltage was applied, an oxidation reactionoccurred in turn, and the EC layer changed from blue back totransparent. In the EC element of Example 3, when a voltage was applied,an oxidation reaction of the compound 4 occurred on one of theelectrodes and a reduction reaction of ethyl viologen occurred on theother electrode to cause coloration. In addition, the compound 4 wasreduced and ethyl viologen was oxidized to cause decoloration when theelement was allowed to short out or a reverse voltage was applied afterthe coloration.

FIG. 11 is graph for showing a relationship between the absorbancechange of the EC element and the drive time. In FIG. 11, a line “a”indicates a change with time in absorbance when the drive voltage of 1.5V was applied at the time of coloring and the drive voltage of 0 V wasapplied at the time of decoloring. The absorbance is a value obtained atthe wavelength of 500 nm, where the compound 4 exhibits absorption.Further, in FIG. 11, a line “b” indicates a change with time in squareof the absorbance indicated by the line “a”. As can be seen from theline “b”, it is revealed that in the coloring direction, there is asuitable linear relationship between the square of the absorbance andthe drive time. This is because the EC element, in particular, theorganic EC element, was rate-controlled by the diffusion of a materialunder the constant voltage as described above.

That is, in the accelerated drive in the coloring direction, byperforming control so that the period of the accelerated drive satisfiesa relationship of Formula (a), it is possible to control thetransitional state in which the light transmittance changes, therebysuppressing an excessive absorbance change.

$\begin{matrix}{T_{m} \leq {\left( \frac{\Delta \; Q_{m}}{\Delta \; Q_{n}} \right)^{2}T_{n}}} & (a)\end{matrix}$

Further, the control of the period of the transitional state can also beachieved as follows. Specifically, based on (ΔQ)²/t, which is the slopeof the line that is obtained by linearly approximating the relationshipbetween the square of the absorbance change amount ΔQ and the time t ofacceleration in the accelerated drive in the coloring direction, thedrive time t₁ required to increase the absorbance from the currentabsorbance to the target absorbance is calculated. Then, the period t₀of the accelerated drive is set so as to satisfy t_(A)≦t₁.

Example 4

In Example 4, as the EC layer 7, a solution obtained by dissolving thecompound 1 in a propylene carbonate solvent together with a supportingelectrolyte (TBAP) was injected. The concentration of the compound 1 was10 mM, and other element constructions were the same as in Example 1.

FIG. 12 is a graph for showing a relationship between the absorbancechange and the drive time in the decoloring direction when, after theorganic EC element was saturated in the coloring direction, the dutyratio was decreased in a stepwise manner under the state in which thedrive voltage of 2.0 V was applied.

As shown in FIG. 12, the organic EC element changed its absorbance to bereached depending on the duty ratio, and even in the decoloringdirection, the light transmittance was able to be controlled by thecontrol of the duty ratio. Further, as the duty ratio became smaller, anamount and speed of change in absorbance became larger, and time spentfor the transitional state became shorter.

From this result, by performing the accelerated drive at the duty ratioD4 smaller than the duty ratio D3 before the normal drive at the dutyratio D3 for maintaining the absorbance at the target absorbance, it ispossible to enhance the operating performance in the decoloringdirection.

Example 5

In the investigation made by the inventors of the present invention,depending on a material to be used, the generated cations causedassociation in some cases. A material that causes association showsdifferent behaviors of an absorption change between cations and cationsin an associated form at the time of coloring and decoloring. As aresult, the absorption spectrum greatly changes in some cases.

In the EC element 1 of Example 5, as the EC layer 7, a solution obtainedby dissolving the compounds 1 and 2 in a propylene carbonate solventtogether with a supporting electrolyte (TBAP) was injected. Theconcentrations of the compounds 1 and 2 were 13.5 mM and 30 mM,respectively, and other element constructions were the same as inExample 1. The compounds 1 and 2 were each an organic EC material inwhich an influence of association formation was not visually observed.

In an EC element 2 of Example 5, as the EC layer 7, a solution obtainedby dissolving the compound 3 and the compound 4 in a propylene carbonatesolvent together with a supporting electrolyte (TBAP) was injected. Theconcentrations of the compound 3 and the compound 4 were 7.5 mM and 10mM, respectively, and other element constructions were the same as inExample 1. The compound was an organic EC material in which an influenceof association formation was not visually observed, and the compound 4was an organic EC material that causes association.

FIG. 13A and FIG. 13B are graphs each for showing a change with time inabsorbance of the element 1 at the time of coloring and decoloring, andFIG. 13C and FIG. 13D are graphs each for showing a change with time inabsorbance of the element 2 at the time of coloring and decoloring. Avoltage of 2.3 V was applied between the electrodes for 25 seconds atthe time of coloring, and a voltage of 0 V was applied therebetween for60 seconds at the time of decoloring.

FIG. 13A is a graph for showing a change with time in absorbance at thetime of coloring and decoloring at the absorption wavelengths of thecompounds 1 and 2. Wavelengths of 540 nm and 600 nm correspond toabsorption peaks of cation species of the compound 1, and wavelengths of450 nm and 490 nm correspond to absorption peaks of cation species ofthe compound 2. In addition, FIG. 13B is a graph for showing a changewith time in absorbance normalized with respect to a time point at whichthe absorbance is maximized (after about 25 seconds) for the respectivewavelengths. It is revealed that the normalized absorbances of therespective materials at the respective wavelengths show relativelymatching behavior at the time of coloring and decoloring.

FIG. 13C is a graph for showing a change with time in absorbance at thetime of coloring and decoloring at the absorption wavelengths of thecompounds 3 and 4. A wavelength of 540 nm is considered to correspond toan absorption peak of cation species of the compound 4, and a wavelengthof 490 nm is considered to correspond to an absorption peak of cationspecies of the compound 4 causing association with each other. Awavelength of 600 nm corresponds to an absorption peak of cation speciesof the compound 3. In addition, FIG. 13D is a graph for showing a changewith time in absorbance normalized with respect to a time point at whichthe absorbance is maximized (after about 25 seconds) for the respectivewavelengths. It is revealed that the normalized absorbances of therespective materials at the respective wavelengths show differentbehaviors at the time of coloring and decoloring. In particular,distortion at the time of decoloring is large. The absorbance isdistorted nearly doubly depending on time. It is considered thatsecondary behavior of generated cations causing association with eachother has an influence.

As described above, in the organic EC element including a plurality ofkinds of EC materials, the case where the EC materials are formed onlyof materials that do not cause association is preferred because theabsorption spectra can be maintained in one or both of a coloringdirection and a decoloring direction.

In the organic EC element formed of a material that does not causeassociation, by performing the accelerated drive at the duty ratio D2larger than the duty ratio D1 before the normal drive at the duty ratioD1 for maintaining the target absorbance, it is possible to enhance theoperating performance in the coloring direction. Further, by performingthe accelerated drive at the duty ratio D4 smaller than the duty ratioD3 before the normal drive at the duty ratio D3 for maintaining thetarget absorbance, it is possible to enhance the operating performancein the decoloring direction.

Example 6

In Example 6, as anodic EC materials, metallocene derivatives; aromaticamine derivatives such as phenazine derivatives, triphenylaminederivatives, phenothiazine derivatives, phenoxazine derivatives; pyrrolederivatives; pyrazoline derivatives other than thiophene derivativeswere used.

Single material or plural materials between the same derivatives orplural materials between the different derivatives were used for theorganic EC element.

By performing the accelerated drive at the duty ratio D2 larger than theduty ratio D1 before the normal drive at the duty ratio D1 for causingthe absorbance to reach the target absorbance and maintaining the targetabsorbance, it was possible to enhance the operating performance in thecoloring direction.

And by performing the accelerated drive at the duty ratio D4 smallerthan the duty ratio D3 before the normal drive at the duty ratio D3 formaintaining the absorbance at the target absorbance, it was possible toenhance the operating performance in the decoloring direction.

Example 7

In Example 7, as cathodic EC materials, anthraquinone-based compounds;ferrocenium salt-based compounds; styryl-based compounds other thanviologen-based compounds were used.

Single material or plural materials between the same derivatives orplural materials between the different derivatives were used for theorganic EC element.

By performing the accelerated drive at the duty ratio D2 larger than theduty ratio D1 before the normal drive at the duty ratio D1 for causingthe absorbance to reach the target absorbance and maintaining the targetabsorbance, it was possible to enhance the operating performance in thecoloring direction.

And by performing the accelerated drive at the duty ratio D4 smallerthan the duty ratio D3 before the normal drive at the duty ratio D3 formaintaining the absorbance at the target absorbance, it was possible toenhance the operating performance in the decoloring direction.

Example 8

In Example 8, as anodic EC materials, thiophene derivatives; metallocenederivatives; aromatic amine derivatives such as phenazine derivatives,triphenylamine derivatives, phenothiazine derivatives, phenoxazinederivatives; pyrrole derivatives; pyrazoline derivatives were used.

And as cathodic EC materials, anthraquinone-based compounds; ferroceniumsalt-based compounds; styryl-based compounds other than viologen-basedcompounds were used.

The combinations between one anodic material and one cathodic materialor plural anodic materials and one cathodic material or one anodicmaterial and plural cathodic materials or plural anodic materials andplural cathodic materials were used for the organic EC element.

By performing the accelerated drive at the duty ratio D2 larger than theduty ratio D1 before the normal drive at the duty ratio D1 for causingthe absorbance to reach the target absorbance and maintaining the targetabsorbance, it was possible to enhance the operating performance in thecoloring direction.

And by performing the accelerated drive at the duty ratio D4 smallerthan the duty ratio D3 before the normal drive at the duty ratio D3 formaintaining the absorbance at the target absorbance, it was possible toenhance the operating performance in the decoloring direction.

According to the one embodiment of the present invention, it is possibleto provide the EC apparatus having an excellent operating performance,which is capable of controlling, during the transitional state in whichthe light transmittance of the EC element changes, the speed and periodof the transitional state in which the light transmittance changes.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2014-159412, filed Aug. 5, 2014, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An apparatus for driving an electrochromicelement, the apparatus being configured to apply a continuous drivepulse to an electrochromic element, the electrochromic element includingan electrochromic layer that contains an electrochromic material and issandwiched between a pair of electrodes, and to change an absorbance ofthe electrochromic element with use of a duty ratio of the continuousdrive pulse, the continuous drive pulse having one cycle including anapplied period of a drive voltage and a stopped period of the drivevoltage, the drive voltage comprising a voltage for causing at least oneof an oxidation reaction of the electrochromic material and a reductionreaction of the electrochromic material, the stopped period comprising aperiod in which, in a closed circuit including the electrochromicelement, a resistor having a resistance value larger than a resistancevalue of another resistor to be connected during the applied period isconnected in series, the duty ratio comprising a ratio of the appliedperiod of the drive voltage to the one cycle, the apparatus beingconfigured to perform, when the absorbance of the electrochromic elementis to be increased from a current absorbance to a target absorbance,before normal drive of driving the electrochromic element at a dutyratio D1 for maintaining the target absorbance, accelerated drive ofdriving the electrochromic element at a duty ratio D2 larger than theduty ratio D1.
 2. The apparatus for driving an electrochromic elementaccording to claim 1, wherein the drive voltage comprises a constantvoltage.
 3. The apparatus for driving an electrochromic elementaccording to claim 1, wherein when arbitrary two absorbance changeamounts of the electrochromic element are represented by ΔQ_(m) andΔQ_(n), and when periods of the accelerated drive that are required forthe arbitrary two absorbance change amounts ΔQ_(m) and ΔQ_(n) arerepresented by T_(m) and T_(n), respectively, the periods of theaccelerated drive are set so as to satisfy a relationship of Formula(a): $\begin{matrix}{T_{m} \leq {\left( \frac{\Delta \; Q_{m}}{\Delta \; Q_{n}} \right)^{2}{T_{n}.}}} & (a)\end{matrix}$
 4. The apparatus for driving an electrochromic elementaccording to claim 1, wherein (ΔQ)²/t, which is a slope of a lineobtained by linearly approximating a relationship between a time t and asquare of a change amount (ΔQ) of the absorbance at a time of theaccelerated drive, is acquired in advance, when the absorbance of theelectrochromic element is to be increased from the current absorbance tothe target absorbance, a time t₁ corresponding to a change amount of theabsorbance is calculated based on the slope, and a period t₀ of theaccelerated drive is set so as to satisfy t_(A)≦t₁.
 5. The apparatus fordriving an electrochromic element according to claim 1, wherein the dutyratio D2 is 100%.
 6. The apparatus for driving an electrochromic elementaccording to claim 1, further configured to perform, when the absorbanceof the electrochromic element is to be decreased from a currentabsorbance to a target absorbance, before normal drive of driving theelectrochromic element at a duty ratio D3 for maintaining the targetabsorbance, accelerated drive of driving the electrochromic element at aduty ratio D4 smaller than the duty ratio D3.
 7. The apparatus fordriving an electrochromic element according to claim 6, wherein the dutyratio D4 is 0%.
 8. The apparatus for driving an electrochromic elementaccording to claim 1, wherein the electrochromic material comprises acomposition in which a plurality of compounds each represented by thefollowing general formula [1] are mixed:

where: B, B′, C, and C′ are each independently selected from an alkylgroup having 1 or more to 20 or less carbon atoms, an alkoxy grouphaving 1 or more to 20 or less carbon atoms, and an aryl group that mayhave a substituent; R₁ represents a hydrogen atom or a substituent; nrepresents an integer of from 1 to 5; and X represents a structurerepresented by the following general formula [2] or [3], and when nrepresents an integer of 2 or more, X's are each independently selectedfrom the structures represented by the following general formulae [2]and [3]:

where: R₂ and R₃ are each independently selected from a hydrogen atom,an alkyl group having 1 or more to 20 or less carbon atoms, an alkoxygroup having 1 or more to 20 or less carbon atoms, an aryl group thatmay have a substituent, and an alkyl ester group having 1 or more to 20or less carbon atoms; R₄ represents an alkylene group having 1 or moreto 20 or less carbon atoms; and when a thiophene ring adjacent to anaromatic ring having the groups B, B′, C, and C′ in the general formula[1] is represented by the general formula [2], R₂ and R₃ each representa substituent other than a hydrogen atom.
 9. An optical filter,comprising: an electrochromic element; and the apparatus for driving anelectrochromic element according to claim
 1. 10. An image pickupapparatus, comprising: the optical filter according to claim 9; and alight receiving element configured to receive light that has beentransmitted through the optical filter.
 11. A lens unit, comprising: theoptical filter according to claim 9; and an optical system comprising aplurality of lenses.
 12. A window member, comprising: an electrochromicelement; and the apparatus for driving an electrochromic elementaccording to claim
 1. 13. A method of driving an electrochromic element,for applying a continuous drive pulse to an electrochromic element, theelectrochromic element including an electrochromic layer that containsan electrochromic material and is sandwiched between a pair ofelectrodes, and changing an absorbance of the electrochromic elementwith use of a duty ratio of the continuous drive pulse, the continuousdrive pulse having one cycle including an applied period of a drivevoltage and a stopped period of the drive voltage, the drive voltagecomprising a voltage for causing at least one of an oxidation reactionof the electrochromic material and a reduction reaction of theelectrochromic material, the stopped period comprising a period inwhich, in a closed circuit including the electrochromic element, aresistor having a resistance value larger than a resistance value ofanother resistor to be connected during the applied period is connectedin series, the duty ratio comprising a ratio of the applied period ofthe drive voltage to the one cycle, the method comprising performing,when the absorbance of the electrochromic element is to be increasedfrom a current absorbance to a target absorbance, before normal drive ofdriving the electrochromic element at a duty ratio D1 for maintainingthe target absorbance, accelerated drive of driving the electrochromicelement at a duty ratio D2 larger than the duty ratio D1.
 14. The methodof driving an electrochromic element according to claim 13, wherein thedrive voltage comprises a constant voltage.
 15. A method of driving anelectrochromic element according to claim 13, further comprisingsetting, when arbitrary two absorbance change amounts of theelectrochromic element are represented by ΔQ_(m) and ΔQ_(n), and whenperiods of the accelerated drive that are required for the arbitrary twoabsorbance change amounts ΔQ_(m) and ΔQ_(n) are represented by T_(m) andT_(n), respectively, the periods of the accelerated drive so as tosatisfy a relationship of Formula (a): $\begin{matrix}{T_{m} \leq {\left( \frac{\Delta \; Q_{m}}{\Delta \; Q_{n}} \right)^{2}{T_{n}.}}} & (a)\end{matrix}$
 16. The method of driving an electrochromic elementaccording to claim 13, further comprising: acquiring in advance,(ΔQ)²/t, which is a slope of a line obtained by linearly approximating arelationship between a time t and a square of a change amount (ΔQ) ofthe absorbance at a time of the accelerated drive; calculating, when theabsorbance of the electrochromic element is to be increased from thecurrent absorbance to the target absorbance, a time t₁ corresponding toa change amount of the absorbance based on the slope; and setting aperiod t₀ of the accelerated drive so as to satisfy t_(A)≦t₁.
 17. Themethod of driving an electrochromic element according to claim 13,wherein the duty ratio D2 is 100%.
 18. The method of driving anelectrochromic element according to claim 13, further comprisingperforming, when the absorbance of the electrochromic element is to bedecreased from a current absorbance to a target absorbance, beforenormal drive of driving the electrochromic element at a duty ratio D3for maintaining the target absorbance, accelerated drive of driving theelectrochromic element at a duty ratio D4 smaller than the duty ratioD3.
 19. The method of driving an electrochromic element according toclaim 18, wherein the duty ratio D4 is 0%.
 20. The method of driving anelectrochromic element according to claim 13, wherein the electrochromicmaterial comprises a composition in which a plurality of compounds eachrepresented by the following general formula [1] are mixed:

where: B, B′, C, and C′ are each independently selected from an alkylgroup having 1 or more to 20 or less carbon atoms, an alkoxy grouphaving 1 or more to 20 or less carbon atoms, and an aryl group that mayhave a substituent; R₁ represents a hydrogen atom or a substituent; nrepresents an integer of from 1 to 5; and X represents a structurerepresented by the following general formula [2] or [3], and when nrepresents an integer of 2 or more, X's are each independently selectedfrom the structures represented by the following general formulae [2]and [3]:

where: R₂ and R₃ are each independently selected from a hydrogen atom,an alkyl group having 1 or more to 20 or less carbon atoms, an alkoxygroup having 1 or more to 20 or less carbon atoms, an aryl group thatmay have a substituent, and an alkyl ester group having 1 or more to 20or less carbon atoms; R₄ represents an alkylene group having 1 or moreto 20 or less carbon atoms; and when a thiophene ring adjacent to anaromatic ring having the groups B, B′, C, and C′ in the general formula[1] is represented by the general formula [2], R₂ and R₃ each representa substituent other than a hydrogen atom.